1. Field of Invention
The present invention relates to a fan device. More particularly, the present invention relates to a centrifugal fan.
2. Description of Related Art
The centrifugal fans are different from the axial fans in that the centrifugal fans intakes air along an axial direction of the impeller and outputs air along a radial direction of the impeller. Referring to FIG. 1, which illustrates a top view of a conventional impeller of the centrifugal fan. The impeller 100 of the centrifugal fan includes a hub 101 and a plurality of blades 102. The blades 102 are arranged radially around the hub 101.
In order to increase the centrifugal fan's performance, e.g. increasing output air volume, one of the solutions is to add more blades 102. When the blades are increased up to a certain number, the blades are crowded in their ends connected to the hub 101. Referring to FIG. 1, when 23 pieces of blades 102 are connected to the hub 101, the blades 102 are crowded in the area around the hub 101. Due to a high density around the hub 101, less air is intake and less air is thus output from the centrifugal fan.
Referring to FIG. 2, which illustrates a cross-sectional view of a conventional fan. One of the solutions is to reduce an axial height of each blade in which dense blades are located, e.g. the upper inclined edge 102a and lower inclined edge 102b near the hub 101, so as to reduce an intake resistance of the dense blades along the axial direction (as shown in the direction of arrows) and increase air expelled along the axial direction of the blade 102.
However, when the axial height on the blades 102 are reduced, the blades 102 are also reduced in their working areas such that the centrifugal fan's performance can be impacted. Therefore, how to reduce the intake resistance of the dense blades and in increase the working areas of the dense blades so as to improve the centrifugal fan's performance even better is a need in designing the centrifugal fan.